linux-kernel - Re: 2.6.25.3: su gets stuck for root

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Message-ID: <4846A9F4.40003@skyrush.com>
Date:	Wed, 04 Jun 2008 08:43:00 -0600
From:	Joe Peterson <joe@...rush.com>
To:	Alan Cox <alan@...hat.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	David Newall <davidn@...idnewall.com>,
	Willy Tarreau <w@....eu>,
	Harald Dunkel <harald.dunkel@...nline.de>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.25.3: su gets stuck for root

Alan Cox wrote:
> On Mon, Jun 02, 2008 at 09:26:48AM -0600, Joe Peterson wrote:
>> P.S.  My stty process sits in "T" - did you say that it would be in "R"
>> if straced and that is correct?
> 
> T would be correct. I'll put together a small diff to printk useful stuff
> when it happens and sent it you tonight/tomorrow

[Alan, thanks for the tips on where to instrument this]

What I have verified so far is that when the problem occurs, it gets to
this point in [tty_io.c] tty_check_change():

1229         kill_pgrp(task_pgrp(current), SIGTTOU, 1);
1230         set_thread_flag(TIF_SIGPENDING);
1231         ret = -ERESTARTSYS;
1232 out:
1233         return ret;

So the error that gets returned to set_termios() is -512.

Also, the various checks before this point (of course) did not pass
(current->signal->tty != tty, !tty->pgrp, task_pgrp(current) ==
tty->pgrp, is_ignored(SIGTTOU), is_current_pgrp_orphaned()).  I have not
printed out the various values from these - let me know if this would be
helpful.  I wanted to pass this info along now in case it is of help.

						-Joe
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